i) Field of the Invention
The present invention relates to a magnetoresistive film indicating a resistance change in accordance with an external magnetic field strength, a magnetoresistive head for utilizing the resistance change of the magnetoresistive film to detect the external magnetic field strength, and an information regeneration apparatus for regenerating information recorded in a recording medium.
ii) Description of Related Art
In recent years, with spread of computers, a large amount of information has been handled in a daily manner. Such information is usually recorded on a recording medium as a large number of physical marks, and regenerated by an information regeneration apparatus for reading the marks on the recording medium to regenerate an electric regeneration signal.
A hard disk drive (HDD) is one of the information regeneration apparatuses, and is characterized in that a memory capacity is large and access speed to the information is fast. The HDD is generally provided with a magnetic disk as the recording medium whose surface is formed of a magnetic material, and a regeneration head for regenerating the information recorded on the magnetic disk. For the magnetic disk, a surface is magnetized for each micro area (one-bit region), and one bit of information is recorded in a form of a magnetization direction of the one-bit region. The regeneration head is disposed in the vicinity of the magnetic disk, and outputs the electric regeneration signal in accordance with a signal magnetic field Hsig generated from the magnetization of the one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
A recording density of the magnetic disk continues to be enhanced year by year, an area of the one-bit region decreases with enhancement of the recording density, and the signal magnetic field Hsig generated from the one-bit region is weakened. Therefore, a magnetic head for outputting a large regeneration signal is necessary even for this weak signal magnetic field Hsig. As the regeneration head for outputting the large regeneration signal, a spin valve magnetoresistive head (SVMR head) which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect starts to be put to practical use in earnest.
The SVMR head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer whose magnetization direction changes in accordance with the external magnetic field, a nonmagnetic middle layer formed adjacent to the free magnetic layer and provided with conductivity, a pinned magnetic layer formed adjacent to the nonmagnetic middle layer and having the magnetization whose direction is fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned magnetic layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned magnetic layer. For the magnetoresistive film, a resistance change is caused in accordance with a relative angle change of magnetization directions of the free magnetic layer and pinned magnetic layer, a resistivity is minimized when the magnetization directions are directed in the same direction, and the resistivity is maximized when magnetizations are directed in opposite directions. The magnetoresistive film is provided with a pair of electrode terminals apart from each other in a film spread direction, and during operation a sense current is passed through the magnetoresistive film from the pair of electrode terminals. While the sense current flows, and the SVMR head is disposed close to a magnetic disk and relatively moved, an electric resistivity of the magnetoresistive film successively changes in accordance with a signal magnetic field Hsig from the magnetic disk, and a regeneration signal with an output voltage represented by a product of the electric resistivity and the sense current value is outputted.
In recent years, for the SVMR head, in order to satisfactorily detect a magnetic field generated from the aforementioned micro one-bit region, an area of the magnetoresistive film is reduced to an order of 0.1xc3x970.1 xcexcm2, and to obtain a high output from the regeneration signal, a thickness of the magnetoresistive film is reduced to an order of several tens of nanometers.
In the magnetoresistive film in the SVMR head, even under normal use conditions of the head mounted on HDD, except the sense current, a large pulse current generated by static electricity sometimes flows. When the large pulse current flows, a temperature of the magnetoresistive film rises. For the magnetoresistive film whose size is reduced as described above, since resistance is large and thermal capacity is small, the temperature is increased to a particularly high temperature by the pulse current. Moreover, the magnetic field is generated with the pulse current, and the magnetoresistive film is exposed to the magnetic field. It is known that when the magnetoresistive film is exposed to the magnetic field in the raised temperature, magnetic destruction, such as magnetization direction change of the pinned magnetic layer and magnitude reduction of the magnetization, easily occurs. When the magnetoresistive film is destroyed, problems such as a remarkable drop of regeneration signal output and an output trouble arise.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a magnetoresistive film high in resistance to destruction, a magnetoresistive head provided with the magnetoresistive film, and an information regeneration apparatus provided with the magnetoresistive head.
In order to attain the aforementioned object, according to the present invention, there is provided a magnetoresistive film comprising a multilayered film including: a bias layer for generating a bias magnetic field; a pinned magnetic layer having magnetization whose direction is fixed by the bias magnetic field generated from the bias layer; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a nonmagnetic middle layer held between the pinned magnetic layer and the free magnetic layer in a thickness direction and indicating a magnitude of resistance in accordance with an angle between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer, and being held between a pair of insulation layers in the thickness direction.
When a current is passed parallel to the magnetoresistive film, a current center as a position of the thickness direction for dividing the current into two so as to obtain respective equal current amounts is positioned on a side including the pinned magnetic layer during dividing of the magnetoresistive film into two in a center position of a layer thickness of the nonmagnetic middle layer in the thickness direction.
For the magnetoresistive film of the present invention, the current center is preferably positioned in the pinned magnetic layer.
For the magnetoresistive film of the present invention, the temperature fails to be prevented from rising, but as compared with the conventional magnetoresistive film, the current center is positioned close to the pinned magnetic layer or on the pinned magnetic layer. In this case, for example, even when a large pulse current attributed to static electricity or the like as described in the related art flows through the magnetoresistive film, a magnetic field strength applied to the magnetization of the pinned magnetic layer is minimized by the pulse current, and therefore any trouble fails to easily occur in the magnetization of the pinned magnetic layer. Therefore, the magnetoresistive film of the present invention is high in resistance to destruction.
In order to attain the aforementioned object, according to the present invention, there is provided a magnetoresistive head, provided with a magnetoresistive film comprising a multilayered film including: a bias layer for generating a bias magnetic field; a pinned magnetic layer having magnetization whose direction is fixed by the bias magnetic field generated from the bias layer; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a nonmagnetic middle layer held between the pinned magnetic layer and the free magnetic layer in a thickness direction and indicating a magnitude of resistance in accordance with an angle between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer, for detecting the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetoresistive head comprises a pair of insulation layers for holding the magnetoresistive film in the thickness direction.
For the magnetoresistive film held by the pair of insulation layers, when a current is passed parallel to the magnetoresistive film, a current center as a position of the thickness direction for dividing the current into two so as to obtain equal current amounts is positioned on a side including the pinned magnetic layer during dividing of the magnetoresistive film into two in a center position of a layer thickness of the nonmagnetic middle layer in the thickness direction.
For the magnetoresistive head of the present invention, the current center is preferably positioned in the pinned magnetic layer.
Since the magnetoresistive head employs the magnetoresistive film of the present invention as the magnetoresistive film, the resistance to destruction of the magnetoresistive film is enhanced, and information regeneration is steadily performed.
In order to attain the aforementioned object, according to the present invention, there is provided an information regeneration apparatus comprising a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded in accordance with a magnetization direction, for detecting the magnetization direction of respective points of the magnetic recording medium, to regenerate the information in accordance with the magnetization direction of the respective points of the magnetic recording medium detected by the magnetic head.
The magnetic head comprises a magnetoresistive film comprising a multilayered film including: a bias layer for generating a bias magnetic field; a pinned magnetic layer having magnetization whose direction is fixed by the bias magnetic field generated from the bias layer; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a nonmagnetic middle layer held between the pinned magnetic layer and the free magnetic layer in a thickness direction and indicating a magnitude of resistance in accordance with an angle between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer, and detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetic head comprises a pair of insulation layers for holding the magnetoresistive film in the thickness direction.
For the magnetoresistive film held by the pair of insulation layers, when a current is passed parallel to the magnetoresistive film, a current center as a position of the thickness direction for dividing the current into two so as to obtain respective equal current amounts is positioned on a side including the pinned magnetic layer during dividing of the magnetoresistive film into two in a center position of a layer thickness of the nonmagnetic middle layer in the thickness direction.
Since the information regeneration apparatus employs the magnetoresistive head of the present invention as the magnetoresistive head, the resistance to destruction of the magnetoresistive film is enhanced, and information regeneration is steadily performed.